More effective demisters on my 1971

The demister tubes hook to the blower box by just sliding over the two outlet flanges. This setup allows much of the air being sent to the demister tubes to spill out into the area behind the consul. This coupled with a weak blower is not up to par here on the rainy and damp west coast.

If these flanges had extensions made for them and an aluminum plate made to cover that elongated oval that they pass thru behind the radio consul. Would that increase the air control and still keep the demister tubes nice and tight so that there is more room for my after market radio?

A pair of the rubber elbows (moss pn 635-520) would then be used to get everything nice and tight.

A relay would also improve the blower speed. There is a place (Princes Auto) that has new surplus blower motors from many different cars. I am making a cardboard template of the blower mounting plate and holes and see if I can find a better one that will work. Perhaps it would be best to clean up a spare heater box and take it with me with me!

The image is my chicken scratch of the idea.

Looks like you are on to something there. I have looked at the tubes, and thought that they could be better myself. I was looking at some aluminum tubing at HD, and thinking if I could make my own tubes to the proper length, it would help the air actually make it up to the windshield. I have also thought of using something other than the paper tubing, maybe even running aluminum box tubing up the firewall, and then transition to round tubing so things will fit together nicely.

I like where you are going with this one.

There were two arrangements of the defogger hoses. I'm trying to remember the differences. It seems to me that the original had ~3" tubes that extended into the heater box and passed through a metal plate. The hoses clamped on the tubes. The later cars had a hoses that sort of clipped in place.

It may be that you have some leakage or kinked hoses. My defogger works fairly well. My heater is like a blast furnace - it will almost burn your feet. I did change my heater motor and I think it was noticeably stronger than the old tired one.

I checked at the local plastics shop. They have 1/8 inch sheet PVC scraps that are in various colours.
The reason for the plate to hold the heater box demister tubes is to ensure that the air onlt has one place to go and nothing can come loose.
By making the air box cover with PVC the tubes can be PVC glued. This would simplify assembly.
The reason for the Moss elbows is to reduce the space that the demister tubes take behind the radio. On a 1971 B there is not much room behind the radio.

I'm in the process of disassembling my '76. By now, any mgb will have air leaks.
The original tubing simply disintegrates. A replacement tube would be an excellent idea.

A simple bit of engineering, but one that makes a big difference.